Medical devices have been used to deliver electrical stimulation therapy to patients to treat a variety of symptoms or conditions, such as chronic pain, tremor, Parkinson's disease, epilepsy, urinary or fecal incontinence, and sexual dysfunction. The electrical stimulation is generally delivered to selected target tissues or locations in a patient's body, such as the brain, the spinal cord, pelvic nerves, or peripheral nerves. Hence, stimulation is used in different therapeutic applications, such as spinal cord stimulation (SCS), deep brain stimulation (DBS), pelvic stimulation, or peripheral nerve stimulation. Medical devices have also been used to deliver electrical stimulation to the heart, e.g., for cardiac pacing, and muscles, e.g., for functional electrical stimulation (FES) to promote muscle movement or prevent atrophy.
Such medical devices typically deliver electrical stimulation therapy in the form of electrical pulses. In many examples, the medical devices that deliver stimulation have been implantable. Implantable medical devices typically deliver electrical stimulation via one or more leads that include electrodes located proximate to target tissues. Implantable medical devices are often able to be communicated with and programmed using an external computing device—referred to a programming device or programmer—that wirelessly and transcutaneously communicates with the implantable medical device.
In most cases, a clinician selects values for a number of programmable parameters in order to define the electrical stimulation therapy to be delivered by the implantable stimulator to a patient. For example, a clinician may select an amplitude value, which may be a current or voltage amplitude, and a pulse width value for a stimulation waveform of the electrical stimulation therapy to be delivered to the patient. In addition, the clinician may also select a pulse rate or frequency for stimulation pulses to be delivered to the patient, a combination of electrodes carried by one or more implantable leads to deliver the stimulation, and the polarities of the selected electrodes. A group of parameters, which can include amplitude, pulse width, pulse frequency, electrode combination and electrode polarity, may be referred to as a program in the sense that they drive the electrical stimulation therapy to be delivered to the patient.
In most cases, a clinician creates the one or more programs that a medical device will use to deliver therapy to a patient during an initial programming session. In the case of implantable medical devices, the initial programming session typically occurs shortly after the device is implanted in the patient. The values for each of the parameters of a program may have a significant impact on the efficacy and side effects of the delivery of therapy according to that program. The process of selecting values for the parameters that provide adequate results can be time consuming. In particular, the process may require a great deal of trial-and-error testing of numerous potential combinations of parameter values before a “best” program is discovered. For example, a “best” program may be a program that is better in terms of clinic efficacy versus side effects experienced than other programs tested. As another example, a best program may also be a program that requires relatively less energy than other programs, such that energy consumed by the electrical stimulation is minimized and power source longevity of the medical device is maximized.
In some cases, the clinician may need to test a large number of possible electrode configurations, i.e., combinations and polarities, in order to identify a desirable configuration. During the testing of an electrode configuration, the clinician may select a pulse width, and then adjust amplitude to identify one or more amplitude thresholds, such as the amplitude at which stimulation is first perceived by the patient (or perception threshold), and the maximum amplitude at which stimulation is still comfortable or the amplitude at which side effects from stimulation become intolerable. A usage range, e.g., a range of amplitudes useable for stimulation therapy, may be defined based on these amplitude thresholds. Additionally or alternatively, the clinician may identify a usage amplitude, which may be an amplitude at which stimulation is effective and results in minimal, tolerable, or no side effects. The clinician may select the pulse-width based on intuition or experience. The clinician may repeat the time-consuming amplitude adjustment process for the electrode configuration with one or more other fixed pulse widths, or may proceed to another electrode configuration after having tested only one pulse width.
Even after this often-lengthy process, the programs selected during an initial programming session may ultimately prove to be inadequate. The eventual inadequacy of the initial programming may be due to a variety of problems, including progression of symptoms and/or an underlying ailment, increased or changed symptoms or side effects during activities and/or postures that were not replicated in the clinic during the initial programming session, slow onset of side effects and, in the case of delivery of stimulation via electrodes located on implantable leads, lead migration. An example of a therapy for which side effects and efficacy are generally not apparent until a program has been applied for an extended period of time is deep brain stimulation.
Patients have been given the ability to adjust stimulation outside of the clinic, at least in part to address such situations. For example, patients with implantable medical devices have been provided an external programming device, referred to as a patient programmer or patient therapy manager, that is simplified relative to the programming device used by a clinician. The patient may use the patient programmer to adjust the stimulation, although often in a manner that is restricted relative to the clinician. In practice, patients often adjust pulse amplitude, without adjusting pulse width, to achieve a desired change in the efficacy or side effects of stimulation.